The present invention relates to a process for the preparation of tricycloundecane derivatives. More particularly, the invention relates to a process for preparing 3-acylamino-4-homoisotwistane (3-acylaminotricyclo[5.3.1.0.sup.3.8 ]-undecane) of the following formula (I): ##STR1## wherein R is alkyl having 1 to 3 carbon atoms, by reacting 4-homoisotwistane (tricyclo[5.3.1.0.sup.3.8 ]undecane) of the following formula (II: ##STR2## with RCN, wherein R is the same as defined above, in the presence of bromine and water.
The desired product of the present invention, i.e., 3-acylamino-4-homoisotwistane of the formula (I), is very valuable as an intermediate. More specifically, 3-amino-4-homoisotwistane hydrochloride obtained by hydrolyzing the compound of formula (I) of the present invention and neutralizing the hydrolysis product has a high antiviral activity [see Japanese Patent Application No. 93968/75 filed by us and J. Med. Chem., 19, 536 (1976)] and is very valuable as a medicinal component or an active component of an animal medicine.
Some processes for the synthesis of 3-acylamino-4-homoisotwistane of formula (I) have already been disclosed by us. For example, there can be mentioned a process in which 4-homoisotwistane (formula II) is reacted with bromine to form 3-bromo-4-homoisotwistane (IV) (see Japanese Patent Application Laid-Open Specification No. 75052/76) and the compound (IV) is reacted with acetonitrile in the presence of sulfuric acid to form 3-acetylamino-4-homoisotwistane (see Japanese Patent Application No. 62814/75), the reactions of this process being schematically illustrated as follows: ##STR3## a process in which 4-homoisotwistane (II) is reacted with a nitrile of the following formula (III): EQU rcn (iii)
wherein R is alkyl having 1 to 3 carbon atoms, in the presence of sulfuric acid and bromine (see Japanese Patent Application No. 145397/76), and a process in which 4-homoisotwistane (II) is reacted with the above-mentioned nitrile (III) and a persulfate in the presence of sulfuric acid (see Japanese Patent Application No. 145396/76).